Method of casting magnesium and alloys thereof



Patented Jan.f31, 1933 I umrsn STATES PATENT OFFICE JOHN A. GANN AND JAMES B. REID, OF MIDLAND, MICHIGAN, ASSIGNORS TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN METHOD OF CASTING MAGNESIUM AND ALLOYS THEREOF Ho Drawing.

The present invention relates to methods of casting readily oxidizable metals, particularly magnesium and alloys thereof wherein the magnesium content predominates. One

' vantages will appear as the description proceeds.

For convenience, the term magnesium is used herein and in the appended claims to mean not only pure ma nesium but also alloys of the same in whic the magnesium content predominates.

Magnesium, as is well known, has a high afiinity for oxygen which is very pronounced when the metal is hot. The casting of this metal in sand molds of the ordinary typeused in casting other metals, such as iron,

, aluminum, copper, is unsatisfactory since the oxygen in the mold acts to oxidize or burn the hot metal, and where the mold is water-bound, as in conventional practice, the metal will decompose the water and combine with the oxygen thereof to such an extent that, if the casting is of relatively heavy section, it may be largely or completely burned up. Many attempts have been made to discover ways of overcoming this difliculty, particularly in an efiort to find suitable agents that could be added to molding compositions, such as water-bound or green sand, which wouldovercome this inherent tendency -of magnesium and its alloys to oxidize and burn when cast. However, in spite of the extensive work done in this field, only a very few agents have been found that can be so used with any de ee P of success. For instance, United States at ent No. 1,825,242 discloses the use of ammonium fluosihcate as an agentto prevent Application filed May 4, 1932. serlal li'o. 609,261.

burning of magnesium in a water-bound sand mold and, at the same time by the chemical action of the protective substance, to produce on the surface of the casting a film of a fluorine compound to increase the resistance to corrosion of the casting. Our experimental work in connection with the aforementioned ammonium fiuosilicate, however, has shown that its use as a protective agent is not wholly satisfactory. For instance, we have found that the effective life of this agent in the sand is comparatively limited. owing to its volatile nature and its tendency to decompose, thereby liberating ammonia, especially when the sand is heated during the casting process. This necessitates frequent re-addition of the agentto the molding sand mixture in order to maintain its-effectiveness to prevent burning of the metal. Moreover, accurate mold impressions in molding sand containing this agent may not easily be retained owing to the sand mixture swelling due to chemical reactionbetween the agent and the wet sand.

As a result of further investigation, we have now made the discovery that amore satisfactory water-bound sand mold for easting magnesium can be produced from molding sand which has been treated with arelativelyv small amount of afl'uosilicate of one of the metals magnesium, lead, sodium, or aluminum. These salts are relatively stable and are not vaporized out of the molding material at the-temperatures existing in the sand molds in which magnesium is cast. Accordingly, the foundry sand which has been treated with a metallic fluosilicate may be used repeatedly without becoming materially impoverished with respect to the protective agent. Numerous tests with water-bound molds made from foundry sand treated with a metallic fluosilicate of the character in hand definitely show that castings which cannot ordinarily be made without imperfections where other agents, such as ammonium salts, sulphur, or boric acid, are used, can be satisfactorily cast where our aforementioned metallic fluosilic ates are used, as hereinafter set forth.

Accordingly," the present invention pro- 100 vides a procedure for casting readily oxidizable meals, such as magnesium, in waterbound temporary molds, whereby burning of the metal is prevented. The invention likewise includes an improved water-bound mold for use in casting such metals. To the accomplishment of the foregoing and related ends, the invention, then, consists of the method and improved molds hereinafter l0 in the claims, the following description setting forth in detail several forms of molds and modes illustrating, however, but several of the various ways in which the principle of the invention may be used.

While the pres'entinvention is applicable for use in connection with various molding materials (sand, carbon, graphite, etc.) for metal casting in general, we will, for simplic- 20 ity, describe the invention in terms" of using our improved oxidation inhibitor agents in water-bound green (plastic) sand molding compositions.

The principle of our invention comprises providing, at least in surface ex osure in the mold, one of the metallic fluoslicates, viz., aluminum fluosilicate, Al (S iF lead fiuosilicate, PbSiF 2H O; magnesium fluosilicate, MgsiF fiH O; sodium fluosilicate, Na SiF A preferable mode of carrying out our invention consists in forming an intimate mixture of the molding material and a relatively small amount of a compound abovementioned, temperin the mixture with 35 water, forming said mlxture into a mold, and

then casting magnesium therein, In addition to said mode of procedure, we may further apply to the inner surfaces of the mold said agents in powder form or in the form of an aqueous solution or emulsion of the same.

The amount of such metallic fluosilicates to mix with the molding composition depends to some extent upon the nature of the casting to be made and the quality of the-molding material. In making large castings it is preferable to employ a greater proportion of the inhibitor than when relatively small castings are made. However, since our new agents are comparatively stable and do not decompose to any material extent when heated in the mold, satisfactory small castings may be made in the sand repared for making large castings, thus 0 viating the need for havin dilferent batches of molding sand mixtures or each class of casting. The actual quantity of one or more of the agents, viz., aluminum fluosilicate, lead fluosilicate, magnesium fluos'ilicate, sodium fluosilicate, to incorporate in the moldin material may vary from to 1 to 10 per cent y weight of the sand or other. suitable molding material according to the size of the casting. Under.

ordinary conditions, an amount of the a ent greater than the minimum stated shoul be 5 unless the casting be made of relatlvely fully described and particularly pointed out l thin section throughout. The maximum stated, on the other hand, is adapted for use mainly in the production of castings of exceptionally heavy section throughout. The preferable amount to use is from 2 to 6 per cent, and the addition of approximately 4 per cent, which is well adapted to meet ordinary casting needs, enables sound cleancasten employing such agents as a mixture of more than one of thesame, the total quantity of such mixture added to the molding matein s to be made in water-bound sand'inolds.

rial may be preferably within limits specified above.

Naturally the effectiveness of any oxidation inhibitor for use as hereinbefore describedvaries with the permeability of the sand, being somewhat greater with sands of high permeability than with those of relatively low permeability. The molding sand should, therefore, be sufficiently open or permeable to permit of free escape of gases out of the .mold, which are formed bycon'tact with the hot metal as it is poured into the mold. In general we have found that a permeability factor. of 30 or more gives satisfactory results, although in many cases good results may be obtained with sands of somewhat lower permeability, The definition of the term permeability as used herein and the method of measuring its numerical value is described in the bulletin Testing and Grading FoundrySands, published by the American Foundrymens Association, March 1931.

i The protective eifect of our new agents is materially greater than that, of ammonium fluosilicate. For example, a magnesium casting weighing 9 pounds was cast in a waterbound sand mold to which was added 3 per cent of ammonium fluosilicate. Result:

'castin showed surface defects in the form of dation inhibitor need not be limited alone to those disclosed, inasmuch as other sand addition agents which are known to give a substantial amount of protection against 0x1- dation of magnesium may be used in con] unction with \the improved agents hereinbefore described. v

Other modes of applying the (principle of our inventionmay e employe those explained, change being made as regards the means and steps herein disclosed,

instead of nesium or an alloy thereo which comprises" casting the metal in a water-bound tem o rary mold having on the surface thereo relatively small amount-of a compound selected from the grou consisting of aluminum fluosilicate, lead uosilicate, magnesium fluosilicate, sodium fluosilicate.

' 2. The method of makin acasting of magnesiumor an alloy thereo which-comprises forming an intimate mixture of foundry sand and a relatively small amount of a compound selected from the group consisting of aluminum fluosilicate, lead fluosilicate, magnesium fluosilicate, sodium fluosilicate, formmg said mixture into a mold, and castingv magnesium therein. I

-3. The method of making a casting of magnesium or an alloy thereof which comprises forming an intimate mixture of foundry sand tempered with water and a relatively small amount of a com ound selected from the group consisting of a uminum fluosilicate, lead fluosilicate, magnesium fluosilicate, sodium fluosilicate, forming said mixture into a mold, and casting magnesium therein.

4. The method of makin a casting of magnesium or an alloy thereof which comprises forming an intimate mixture of foundry sand tempered with water and a compound selected from the group consisting of aluminum fluosilicate, lead fluosilicate, ma esium fluosilicate, sodium fluosilicate, forming said mixture into a mold, applying acompound named in the said group to the inner surface of the mold, and casting magnesium therein.-

The method of making a casting of magnesium or an alloy thereof which comprises forming an intimate mixture of foundry sand tempered with water and from 1 to 10 per cent of a compound selected from the group consisting of aluminum fluosilicate, lead fluosilicate, magnesium fluosilicate, sodium fluosilicate, forming said mixture into a mold, and casting magnesium therein. 6. The method of making a casting of magnesium or an alloy thereof which comprises forming an intimate mixture of foundray sand tempered with water and from2 to 6 per cent of a compound selected from the group consisting of aluminum fluosilicate, lead fluosilicate, magnesium fluosilicate, sodium fluosilicate, forming said mixture into a mold, and casting magnesium therein.

7. The method of maldng a casting of magnesium or an alloy thereof which comprises forming an intimate mixture of foundry sand tempered with water and ap roximately 4 per cent of a compound selected from the group consisting of aluminum fluesilicate, lead fluosilicate, magnesium fluosilicate, sodium fluosilicate, forming said mixture into a mold, and casting magnesium therein.

8.- The method of making a casting of magnesium or an alloy thereof which comprises forming an intimate mixture of foundry sand tempered with water and from 2 to 6 per cent of aluminum fluosilicate, forming said mixture into a mold, and casting magnesium therein.

9. The method of making a castingiof magnesium or an alloy thereof which comprises forming an intimate mixture of foundry sand tempered with water and from 2 to 6 per cent of lead fluosilicate, forming said. mixture into a mold, and casting magnesium therein.

10. The method of making a casting of magnesium or an alloy thereof which comprises forming an intimate mixture of foundry sand tempered with water and from 2 to 6 per centof magnesium fluosilicate, forming said mixture into a mold, and casting magnesium therein.

11. In a methodof casting magnesium or an alloy thereof the steps which consist in applying to the surface of a water-bound temporary mold a facing comprising a compound selected from the group consisting of aluminum fluosilicate, lead fluosilicate, magnesium fluosilicate, sodium fluosilicate, and casting magnesium in said mold. a 1

12. A mold for casting magnesium or an alloy thereof formed from the mixture which comprises foundry sand tempered with water and intimately mixed with a comopund selected from the group consisting of aluminum fluosilicate, lead fluosilicate, magnesium fluosilicate, sodium fluosilicate.

13. A mold for casting magnesium or an alloy thereof formed from the mixture which comprises foundry sand tempered with water and intimately mixed with from 2 to 6 per cent of a compound selected from the roup consisting of aluminum fluosilicate, vlea fluosilicate, magnesium fluosilicate, so dium fluosilicate. L 7

- Signed by us this 29th day of April, 1932.

JOHN A. GANN. JAMES B. REID. 

